1. Field of the Invention
The present invention relates to a passenger detection system that detects whether or not a passenger is sitting on a seat of a vehicle. More specifically, the present invention relates to a method of revising an empty seat reference weight that is used as a standard for determining if there is a passenger on a seat.
2. Background Information
An example of a conventional passenger detection system is described in Japanese Laid-Open Patent Publication No. 9-301120. This passenger detection system is fixed onto a body of a vehicle and has a strain gauge arranged on a rigid portion that holds a seat. When a passenger sits on the seat, the strain gauge detects the deflection of the rigid portion, and thus, detects that a passenger has sat down.
In view of the above, there exists a need for an improved passenger detection system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that the above described passenger detection system determines that a passenger is sitting on the seat when the value outputted from the strain gauge indicates a strain larger than the strain value outputted when no one is sitting on the seat. If, for example, the vehicle body is deformed due to a light collision, the value outputted by the strain gauge when there is no passenger sitting on the seat may be different than it was before the collision. Consequently, since the determination is based on the output value, there is the possibility that the passenger detection system will not be able to accurately determine if a passenger is sitting on the seat or not.
The object of the present invention is to resolve this issue by providing a passenger detection system that can appropriately revise the value outputted from the strain gauge when there is no passenger sitting on the seat to determine with certainty if a passenger is sitting on the seat even after the output value has changed due to the body deformation.
In the present invention, when the weight detected by the weight detecting device decreases from a prior detected weight to a subsequent detected weight that differs there-from by an amount greater than or equal to a prescribed value after the door status has changed from the door closed state to the door open state, the system assumes that a passenger on the seat has exited the vehicle or an object on the seat has been removed and stores the subsequent detected weight (the weight detected after the weight decrease) as the reference weight. Since the difference between the reference weight and the weight detected by the weight detecting device is used to determine if a passenger or object is on the seat, the determination of whether or not there is a passenger or object on the seat can be accomplished accurately.
Moreover, the present invention does not require a special power source for the control means in order to store the empty seat weight because it stores the subsequent detected weight as the reference weight when the ignition switch is in the ON state.
Thus, the present invention can grasp with certainty the timing at which the seat entered the empty state indicated by the reference weight because it determines that a person or object has exited the vehicle when the following occurs: the ignition switch changes from the ON state to the OFF state, then the door status changes from the closed state to the open state, and finally the weight detected by the weight detecting device decreases by an amount greater than or equal to a prescribed value.
Thus, the present invention, the period of time over which power must be supplied to store the reference weight can be limited because the reference weight is stored when the first condition is established within a first prescribed time period after the ignition switch changes from the ON state to the OFF state.
The present invention can store the reference weight (which corresponds to the empty seat state) only when a passenger exits the vehicle immediately after a door opens because it stores the reference weight within a second prescribed time period after the door status changes from the closed state to the open state.
The present invention stores a third detected weight, which is the weight detected by the weight detecting device when the ignition switch detected by the ignition detecting means changes from the OFF state to the ON state, as the reference weight when the third detected weight is negative. Consequently, when the weight detected by the weight detecting device is negative, the system determines that there is no passenger or object on the seat and stores the third detected weight as the reference weight.
The present invention executes statistical processing on a prescribed number of second and/or third detected weights and stores the result as the reference weight corresponding to the empty seat state. Consequently, measurement error of the weight detecting device and error caused by inconclusive operations when passengers enter and exit the vehicle can be suppressed.
The foregoing can basically be attained by a passenger detection system comprising a weight detecting device, a door status detecting device, a storage device and a determining device. The weight detecting device is arranged and configured to detect weight on a seat. The door status detecting device is arranged and configured to detect open/closed door status of a vehicle door. The storage device is arranged and configured to store a reference weight, the reference weight being set to a subsequent detected weight if the subsequent detected weight is lighter than a prior detected weight by an amount greater than or equal to a prescribed value after a first condition has been established indicating that the door status detected by the door status detecting device has changed from a door closed state to a door open state, and a second condition has been established indicating that the weight detected by the weight detecting device has changed from the prior detected weight to the subsequent detected weight. The determining device is arranged and configured to determine if an object is present on the seat based on a difference between current detected by the weight detecting device and the reference weight stored in the storage device.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.